1. Field of the Invention
This invention relates to the separation of digestible carbohydrate components from the indigestible carbohydrate components of oat, barley, or combinations of grain products and also relates to conversion of these components to cereal hydrocolloidal soluble fiber and protein-enhanced compositions that are useful as texturizers and nutrients for improving the health benefits of foods.
Cereal grains contain large quantities of digestible starch along with proteins, lipids, ash, and indigestible components. The indigestible components are called dietary fibers that are the soluble and insoluble components of cell walls. They are resistant to endogenous digestion in the human upper digestive tract [Am. J. Clin. Nutr., 25: 464-465 (1972)]. Such fibers consist primarily of cellulose, hemicellulose, pectin substances, oligosaccharides, lignin, gums and mucilages and have been an important food component since early times. Diets containing significant amounts of dietary fiber are known to assist in the digestive process and contribute to improved health. Burkitt et al. [Lancet, 2: 1408-1411 (1972)] teach that dietary fiber has a role in the prevention of certain large-intestine diseases, including cancer of the colon and diverticulitis. Burkitt et al. also indicate that serum cholesterol rises when dietary fiber is removed from the diet, and that eating a fiber-rich diet lowers serum cholesterol. Trowell [Am. J. Clin. Nutr., 25: 464-465 (1972)] and Dreher [Handbook of Dietary Fiber, An Applied Approach, Marcel Dekker, Inc., New York, N.Y. (1987)] have reported on similar conclusions regarding the relationship between fiber and health benefits.
It is now known that soluble and insoluble fibers provide different health benefits. For example, wheat bran is very rich in insoluble crude fiber (mainly cellulose and hemicelluloses) and is excellent for decreasing the transit time of food through the digestive tract [Anderson et al., Am. J. Clin. Nutr., 32: 346-363 (1979)]. Some soluble fibers, especially β-glucan, are reported to reduce total plasma cholesterol [Behall et al., J. Am. Coll. Nutr., 16: 46-51 (1997)].
Diet has been recognized as a major factor in diabetes mellitus treatment since the discovery of insulin. Over many years, the calorie contributing components in the diet have shifted among the portions of digestible carbohydrates, proteins, and fat. Early recommendations were to limit dietary digestible carbohydrates. These low-carbohydrate diets with high-fat, mainly saturated fats, were associated with dyslipidemias and cardiovascular disease. More recently, the American Diabetes Association (ADA) recommended a diet in which protein contributes 10% to 20% of the total calories. The ADA recommends that saturated fat should contribute less than 10% of total calories, and polyunsaturated fat contributing no more than 10% of total calories, with the remainder of fat calories coming from monounsaturated fat. Fiber intake is recommended to be approximately 20 to 35 g/day.
There is a need in the art for a dietary fiber food ingredient with decreased carbohydrate (particularly starch) digestible components that is functionally useful in foods and acts to delay the absorption curve of digestible carbohydrates after a meal. The ingredient should be capable of being easily incorporated into food products without interfering with taste and texture. The functional properties of the ingredient should have about the same rheological qualities as the original starting material with its higher starch component. It is also important in the art to provide nutrients for several health benefits including heart diseases and diabetes Type 2.
2. Description of the Prior Art
Dietary fiber typically consists of morphologically intact cellular tissues of various seed brans, hulls, and other agricultural by-products that have a high content of crude fiber [Dintzis et al., Cereal Chem., 56:123-127 (1979)]. When added to foods, these fibers impart a gritty texture to the final product. One solution to this problem has been to grind the fibers to give finer powders, but these powders still lack smooth hydrocolloidal character. Also, the alkaline or alkaline/peroxide treatment of agricultural byproducts as reported by Gould (U.S. Pat. Nos. 4,649,113 and 4,806,475), Gould et al. (U.S. Pat. No. 4,774,098), Ramaswamy (U.S. Pat. No. 5,023,103); and Antrim (U.S. Pat. No. 4,038,481) does not remove the crude fiber components but completely eliminates the soluble fiber components. Morley et al. (U.S. Pat. No. 4,565,702) and Sharma (U.S. Pat. No. 4,619,831) teach enrobing the high crude fiber insoluble dietary fibers with soluble fibers (gums) for providing better texture and mouth feel.
Soluble fibers are water-soluble polysaccharides such as pectin-like fruit and beet by-products (Thibault et al., U.S. Pat. No. 5,275,834). There have been a number of reports of alkaline extraction of agricultural materials, including hulls and brans, for obtaining their soluble hemicellulose components (Wolf, U.S. Pat. No. 2,709,699; Rutenberg et al., U.S. Pat. No. 2,801,955; and Gerrish et al., U.S. Pat. No. 3,879,373).
Gould et al., U.S. Pat. No. 4,497,840, describe foods made from oat bran which contains at least 150% more crude fiber than whole oat flour. Also, Murtaugh et al., U.S. Pat. No. 4,908,223, show grinding oat bran and rice products to make frozen desserts without any separation of crude fiber components. Rudel, U.S. Pat. No. 4,961,937, also used non-separated oat products in baked products.
The oat soluble fiber, also called oat gum or β-glucan, of the oat groat was fractionated as a separate component by an extensive series of separation described by Hohner and Hyldon, U.S. Pat. No. 4,028,468. Another wet-milling of oats to give various fractions including oat proteins was described by Cluskey et al. [Cereal Chem., 50:475 (1973)]. Also β-glucan enriched cellulose-containing fiber with little starch was described by Lehtomaki et al., U.S. Pat. No. 5,183,677. Oat β-glucan was water-extracted from oat groat in U.S. Pat. No. 5,512,287 by Wang et al. Also, barley β-glucan was purified by an alkaline extraction procedure of Bhatty (U.S. Pat. No. 5,518,710).
U.S. Pat. No. 4,028,468 to Hohner et al. (1977) outlines a method to extract β-glucan from oat groat. Groats are hulled, usually crushed grain, especially oats. According to Hohner et al., oat groat is flaked, the oil extracted, dried, ground and air classified to produce a coarse milling fraction. The extraction of β-glucan includes mixing the coarse fraction with water, adjusting the pH twice, chilling the water extract to 4° C., and drying recovered β-glucan in a vacuum dryer. The multiple pH adjustments, the use of oil extraction, air classification and vacuum drying are expensive processing steps which make the invention economically disadvantageous from a commercial production point of view. High purity β-glucan fractions, (over 50 percent pure β-glucan) were not reported using this technique.
U.S. Pat. Nos. 4,804,545 (1989) and 5,013,561 (1991), both to Goering et al., outline a method for extracting β-glucan from waxy barley grain. Waxy barley grain is ground and mixed with water, centrifuged to remove bran and starch, boiled to destroy the activity of β-glucanase, centrifuged to remove the coagulated protein which contains a high percentage of oil, and the extract passed through an ultrafilter to purify the β-glucan. The β-glucan solids are dried on a drum dryer or a spray dryer. Recovering the solids using this technique with a drum dryer or a spray dryer produces a light yellowish-brown-colored product with a purity of β-glucan less than 50 percent by weight of the product. These two inventions produce β-glucan products with undesirable β-glucan purity and low molecular weights.
U.S. Pat. Nos. 5,106,640 (1992) and 5,183,677 (1993) both to Lehtomaki et al., describe a method for producing a β-glucan-enriched alimentary fiber from oats and barley. Barley or oat grains are dehulled, optionally ground and slurried in water at about 8° C. with ethanol addition. The slurry is screened and a product is collected. The product contains 15-40 percent β-glucan and about equal amounts of starch and protein. This invention does not produce a β-glucan product having a purity of more than 50 percent by weight of the product.
U.S. Pat. No. 5,512,287 by Wang et al. teaches a method of recovering β-glucan as a white-colored powder containing about 75 percent of the naturally occurring β-glucan in cereal grains with molecular weights of the β-glucan ranging between 400,000 daltons to 2,000,000 daltons.
Potter et al. (U.S. Pat. No. 6,485,945) found that an all aqueous system using ultrafiltration gave solids with high soluble β-glucan contents. Also, when an aqueous solution was heated in an open vessel such as tray evaporator, a thin, solid film, or “skin”, spontaneously formed on the surface of the liquid that was predominantly P-glucan and separated out from a very dilute β-glucan solution.
Previous processes for concentrating soluble β-glucan from cereals such as oats or barley, have been considered to be impractical for application to commercial manufacturing processes because of high cost of processing the high-viscosity, low-concentrations of oat or barley grain solids in aqueous solution. The reliance upon a water-miscible solvent, such as ethanol or isopropanol, to precipitate soluble β-glucan from aqueous solutions by these solvents, entails high in-process losses and difficult reclamation. The low solid contents of the aqueous solutions require huge amounts of solvent for precipitation. If the solids concentration could be elevated, considerable saving could be made.
Inglett (U.S. Pat. No. 4,996,063) teaches that water-soluble dietary fiber compositions are prepared by treatment of milled oat products with α-amylase and removal of insoluble components by centrifugation. In a related development, Inglett (U.S. Pat. No. 5,082,673) teaches that a soluble dietary fiber and maltodextrin-containing product is prepared by hydrolyzing a cereal flour or a blend of cereal flour and starch with an α-amylase. This soluble fiber composition has been described for use in ready-to-eat cereal (Smith and Meschewski, U.S. Pat. No. 5,275,831) and low fat comminuted meat products (Jenkins and Wild, U.S. Pat. Nos. 5,294,457 and 5,585,131).
Also, U.S. Pat. No. 6,060,519 by Inglett discovered a novel class of hydrocolloidal compositions recovered from the liquid fraction obtained by subjecting oat or barley substrates to a heat-shearing treatment. These compositions contain soluble fiber, principally β-glucan, and are substantially free of insoluble fiber particles. The hydrocolloidal products are smooth in texture and display the properties of a dairy cream, coconut cream, or fat imitation on rehydration. They are recovered in about 70-95% yields.
Cahill et al. (U.S. Pat. No. 6,531,178) found that high levels of β-glucan from oat or barley grains could be extracted from an aqueous solution using various pH adjustments at around 6% oat slurry in order to carryout the extraction procedure at temperatures below the gelatinization of starch. Their soluble β-glucan products could be agglomerated for use in foods, and have approximately 50% available carbohydrate content.
Malkki and Myllymaki (U.S. Pat. No. 5,846,590) found that trypsin in a mild treatment of oat products with a proteolytic enzyme leads to an elevation of viscosity of β-glucan of certain varieties. This effect was accentuated by subsequent thermal, solvent and mechanical treatments that resulted in an enrichment of dietary fibers.